no salability and pollutes the atmosphere (SharmaShivappa, 2008). Additionally, environmental pollution caused by dumping or landfilling of waste materials in the environment are among the most crucial
issues the world is facing today (Deepanraj, Sivasubramanian, & Jayaraj, 2017). Normally, the burning,
landfilling, and open dumping methods are used as
treatment methods for organic wastes. Landfilling
results in emissions of methane, carbon dioxide, and
nitrous oxides, which contribute to the greenhouse
effect (Wang, 2010). Currently, the management of
textile wastes involves recycling them as secondhand textiles, filling materials in the textile industry,
composting, landfilling, and burning (Hasanzadeh et
al., 2018). Therefore, the annual global production
of end life textile wastes is increasing, causing an
increased interest in the impact of the disposed of
wastes on the environment. However, textile wastes
are an enriched source of energy and materials (Hasanzadeh et al., 2018). Textile wastes include wastes from
streams of fiber, textile, and clothing manufacturing
process, commercial service, and consumption (Hu et
al., 2018).
Textile wastes mainly consist of cotton and viscose
fibers. Reports from previous studies showed that cotton wastes have a significant potential to be used as
a substrate for the production of different bioenergy
such as biogas (Rasel et al., 2019). The environmental
problems caused by organic wastes should be militated
against. One effective way to avoid these problems
is to use the wastes as a substrate for biogas production (Papacz, 2011). Biogas represents one of the most
important renewable energy sources (Triolo, Pedersen, Qu, & Sommer, 2012). It is possible to mitigate
the negative environmental effects of solid wastes by
using them for the production of biogas. Moreover,
the transformation of complex organic materials into
biogas reduces the emission of greenhouse gases and
can produce by-products like high-value fertilizer for
growing crops (Jeihanipour, Aslanzadeh, Rajendran,
& Balasubramanian, 2013; Treichel et al., 2019). Furthermore, about emissions, biogas production might
be better for the environment than incineration of
organic wastes. Methane from biogas has different
applications. It may be utilized as a source of heat,
steam, electricity and can be upgraded to vehicle fuels
(Papacz, 2011). It may also be used as a household
fuel for cooking and lighting or in fuel cells (Velmurugan, , Deepanraj, & Jayaraj, 2014). Putting all
these advantages into consideration, biogas is one
of the most environmentally friendly energy sources
which could substitute fossil fuels (Manager et al.,
2009). Biogas can be produced from a wide range of
substrates such as industrial, municipal, wastewater,
agricultural, and food wastes as well as plant residues
(Phun et al., 2017). Biogas consists mainly of methane
(40-75%), carbon dioxide (25-60%), and other impurities and the biogas composition exchanges depend on
the type of the substrate (Andriani, Wresta, Atmaja,
& Saepudin, 2014; Rajendran & Balasubramanian,
2011).
Anaerobic digestions (AD) are divided into three
categories depending on the solid contents. The low
solid reactors contain less than 10% total solids (TS)
with a material to water ratio of 1:10 (Kleinheinz &
Hernandez, 2016). The medium solid reactors contain
15-20% TS with a material to water ratio of 1:5-7.
Finally, the high solid reactors have TS of 22-40%
with a material to water ratio of 1:2.5-4.5 (MONNET,
2009). Generally, the organic dry matter content that
is suitable substrates for AD is in a range of 70-95%
of TS. The TS in cotton waste are in this range. The TS
affect the survival growth and activities of microorganisms in anaerobic reactors (Budiyono, Syaichurrozi,
& Sumardiono, 2014). Anaerobic batch reactors of
solid wastes are more useful because they can perform
quick digestion with simple and inexpensive equipment, and can help in assessing the rate of digestion
easily (Khalid, Arshad, Anjum, Mahmood, & Dawson,
2011). Substrates with less than 60% of organic dry
matter content are rarely considered valuable for AD
(Vögeli, Lohri, Gallardo, Diener, & Zurbrügg, 2014).
The performance ofAD process is highly dependent on
the characteristics of substrates as well as the activity
of the microorganisms involved in different degradation steps (Horváth, Tabatabaei, Karimi, & Kumar,
2016). A substrate that provides carbohydrates, proteins, fats, cellulose and hemicelluloses is suitable for
AD (Achinas, Achinas, & Euverink, 2017; Rajendran,
2015).
The optimization of the AD has been mainly concentrated on the operational parameters such as moisture content (MC), TS, VS, mixing, pH, C/N ratio,
loading and retention times, temperature, feedstock
composition, and pre-treatment methods (Ferguson,
Villa, & Coulon, 2014). Facilities that are available
run using mainly industrial wastes as feedstock. Nevertheless, the need for expanding AD to a range of
new substrates has raised attention in key points which
should be taken into consideration when new feedstocks are going to be used. The use of cotton wastes
for the production of high-value compounds including biogas and industrial products provides a means
to overcome disposal issues, reduce consumption of
fossil fuels and mitigate adverse impacts on the environment (Sharma-Shivappa, 2008). From literature,
there is very limited work that has used cotton waste
as a substrate for biogas production (Ismail & Talib,
2016). Isci and Demirer (2007) studied the anaerobic treatability and methane generation potential of
different cotton wastes in batch reactors. Results indicated that cotton wastes can be treated anaerobically
and are a good source of biogas. Given its large
potential for biogas production, cotton certainly merits
more research attention for being used as a feedstock
indigestion with manures. Ismail and Talib (2016)
examined the potential of using recycled medical cotton industry waste as a source of biogas recovery.
Further studying of biogas production from cotton
waste by continuous system and regeneration of alkali
solutions of CO 2 if large amounts are used is needed.
Rasel et al. (2019) studied the cotton waste (spinning,
203
issues the world is facing today (Deepanraj, Sivasubramanian, & Jayaraj, 2017). Normally, the burning,
landfilling, and open dumping methods are used as
treatment methods for organic wastes. Landfilling
results in emissions of methane, carbon dioxide, and
nitrous oxides, which contribute to the greenhouse
effect (Wang, 2010). Currently, the management of
textile wastes involves recycling them as secondhand textiles, filling materials in the textile industry,
composting, landfilling, and burning (Hasanzadeh et
al., 2018). Therefore, the annual global production
of end life textile wastes is increasing, causing an
increased interest in the impact of the disposed of
wastes on the environment. However, textile wastes
are an enriched source of energy and materials (Hasanzadeh et al., 2018). Textile wastes include wastes from
streams of fiber, textile, and clothing manufacturing
process, commercial service, and consumption (Hu et
al., 2018).
Textile wastes mainly consist of cotton and viscose
fibers. Reports from previous studies showed that cotton wastes have a significant potential to be used as
a substrate for the production of different bioenergy
such as biogas (Rasel et al., 2019). The environmental
problems caused by organic wastes should be militated
against. One effective way to avoid these problems
is to use the wastes as a substrate for biogas production (Papacz, 2011). Biogas represents one of the most
important renewable energy sources (Triolo, Pedersen, Qu, & Sommer, 2012). It is possible to mitigate
the negative environmental effects of solid wastes by
using them for the production of biogas. Moreover,
the transformation of complex organic materials into
biogas reduces the emission of greenhouse gases and
can produce by-products like high-value fertilizer for
growing crops (Jeihanipour, Aslanzadeh, Rajendran,
& Balasubramanian, 2013; Treichel et al., 2019). Furthermore, about emissions, biogas production might
be better for the environment than incineration of
organic wastes. Methane from biogas has different
applications. It may be utilized as a source of heat,
steam, electricity and can be upgraded to vehicle fuels
(Papacz, 2011). It may also be used as a household
fuel for cooking and lighting or in fuel cells (Velmurugan, , Deepanraj, & Jayaraj, 2014). Putting all
these advantages into consideration, biogas is one
of the most environmentally friendly energy sources
which could substitute fossil fuels (Manager et al.,
2009). Biogas can be produced from a wide range of
substrates such as industrial, municipal, wastewater,
agricultural, and food wastes as well as plant residues
(Phun et al., 2017). Biogas consists mainly of methane
(40-75%), carbon dioxide (25-60%), and other impurities and the biogas composition exchanges depend on
the type of the substrate (Andriani, Wresta, Atmaja,
& Saepudin, 2014; Rajendran & Balasubramanian,
2011).
Anaerobic digestions (AD) are divided into three
categories depending on the solid contents. The low
solid reactors contain less than 10% total solids (TS)
with a material to water ratio of 1:10 (Kleinheinz &
Hernandez, 2016). The medium solid reactors contain
15-20% TS with a material to water ratio of 1:5-7.
Finally, the high solid reactors have TS of 22-40%
with a material to water ratio of 1:2.5-4.5 (MONNET,
2009). Generally, the organic dry matter content that
is suitable substrates for AD is in a range of 70-95%
of TS. The TS in cotton waste are in this range. The TS
affect the survival growth and activities of microorganisms in anaerobic reactors (Budiyono, Syaichurrozi,
& Sumardiono, 2014). Anaerobic batch reactors of
solid wastes are more useful because they can perform
quick digestion with simple and inexpensive equipment, and can help in assessing the rate of digestion
easily (Khalid, Arshad, Anjum, Mahmood, & Dawson,
2011). Substrates with less than 60% of organic dry
matter content are rarely considered valuable for AD
(Vögeli, Lohri, Gallardo, Diener, & Zurbrügg, 2014).
The performance ofAD process is highly dependent on
the characteristics of substrates as well as the activity
of the microorganisms involved in different degradation steps (Horváth, Tabatabaei, Karimi, & Kumar,
2016). A substrate that provides carbohydrates, proteins, fats, cellulose and hemicelluloses is suitable for
AD (Achinas, Achinas, & Euverink, 2017; Rajendran,
2015).
The optimization of the AD has been mainly concentrated on the operational parameters such as moisture content (MC), TS, VS, mixing, pH, C/N ratio,
loading and retention times, temperature, feedstock
composition, and pre-treatment methods (Ferguson,
Villa, & Coulon, 2014). Facilities that are available
run using mainly industrial wastes as feedstock. Nevertheless, the need for expanding AD to a range of
new substrates has raised attention in key points which
should be taken into consideration when new feedstocks are going to be used. The use of cotton wastes
for the production of high-value compounds including biogas and industrial products provides a means
to overcome disposal issues, reduce consumption of
fossil fuels and mitigate adverse impacts on the environment (Sharma-Shivappa, 2008). From literature,
there is very limited work that has used cotton waste
as a substrate for biogas production (Ismail & Talib,
2016). Isci and Demirer (2007) studied the anaerobic treatability and methane generation potential of
different cotton wastes in batch reactors. Results indicated that cotton wastes can be treated anaerobically
and are a good source of biogas. Given its large
potential for biogas production, cotton certainly merits
more research attention for being used as a feedstock
indigestion with manures. Ismail and Talib (2016)
examined the potential of using recycled medical cotton industry waste as a source of biogas recovery.
Further studying of biogas production from cotton
waste by continuous system and regeneration of alkali
solutions of CO 2 if large amounts are used is needed.
Rasel et al. (2019) studied the cotton waste (spinning,
203